1. Field of the Invention
The present invention is directed to providing a printer; specifically a wide format digital printer that is capable of printing onto both roll stock and onto single sheets of discontinuous substrate and to providing a novel mechanism for moving the feed rollers of the printer to facilitate quality printing on both types of substrate.
2. Brief Description of the Art
Digital printing is widely used for printing posters, wall decorations, signs and the like. The material to be printed, if flexible, is typically provided on a continuous roll and is advanced roll to roll past the print head. Sometimes however, particularly when printing onto a rigid material, the material to be printed is provided in sheet form and the printing technique is then known as flat bed printing. The wider the sheet, the greater the tendency for it to be warped or misaligned whilst being fed past the printer head, and with wide/super wide printing, here the print are is 3 m wide or more, flat bed printing is only suitable or printing onto rigid substrates.
In all printing technologies advancing systems are required to accurately position the material to be printed with respect to the printing head. Even a small deviation from the correct positioning results in noticeable printing defects.
To save space and equipment costs, it is useful for a single machine to be able to operate as both a flat bed printer and as a roll to roll printer. The wider the material to be printed, the more difficult it is to obtain alignment, and providing a single printer, capable of both flat bed and roll to roll printing, though desirable, is not easily achieved.
WO04037543 to Nur Macroprinters LTD., titled “Advancing System and Method for a Digital Printing Apparatus”, describes a printer apparatus comprising a printing head system and an advancing system. The printing head includes a print head assembly mounted for movement along at least one horizontal axis with respect to a printing area. The advancing system is configured and operable for enabling to selectively locate the printing area in either one of a first or a second printing plane arranged in vertically spaced-apart relationship, thereby selectively exposing the first or second printing plane to the print head assembly for printing. The first and second printing planes are defined by, respectively, a first flat-bed assembly and a second roll-to-roll assembly of the advancing system.
Nur Macroprinter's solution requires moving the printer head from one printing plane to another. In each printing mode the printer head moves over a relatively long table in two directions. The two printing modes use different printing tables. Moving from one printing mode to another in this manner is likely to be time consuming. Furthermore, since the printer head may be moved in three directions with respect to the substrate to be printed, it is not easy to ensure accurate, repeatable alignment, particularly when moving from one printing type to the other. Because two printing tables are used, both require calibrating to attain planarity in a parallel plane to the movement of the printer head, and this is not easily achieved since the printing tables have a tendency to warp. Indeed movement of the printing table is best avoided.
U.S. Pat. No. 6,296,403 to Scitex Vision describes a dual-mode printer for printing on both flexible and rigid substrates that includes a table for providing a substantially planar support surface for supporting a substrate thereupon. A flexible-substrate feed system is configured to feed a flexible substrate in a given feed direction across the support surface. The printer has a print head configured for depositing a printing medium on a substrate as part of a printing process. A motion system is configured to generate relative displacement between the print head and the support surface in at least a first direction parallel to the feed direction. This combination of components allows the printer to be used in both: (i) a flexible-substrate mode in which relative displacement between the substrate and the print head is generated at least in part by the flexible-substrate feed system, and (ii) in a rigid-substrate mode in which relative displacement between the substrate and the print head is generated exclusively by the motion system.
The printing table of the dual mode printer used is a long table suitable for flat bed printing. Such a table is inherently unsuitable for roll-to-roll printing since the distance between the rollers is large, and the flexible substrate to be printed is likely to assume a wavy surface which adversely affects the resolution of the printing thereon.
Russian Patent Number RU 2167063 relates to a method of printing wherein the substrate to be printed is fed roll to roll and the table moves as well.
WO05074519 to L & P Property Management Company describes an apparatus and a method of ink jet printing that use a system for feeding a substrate longitudinally relative to a support area, and a system for moving a print head parallel to the direction of the substrate feed. Indexing between transverse scan rows of a print head is carried out initially by the substrate feed system and the actual feed distance is measured using an encoder or other substrate position measurement device. A controller determines the amount of any error that occurs between the actual and the desired feed distances. The controller then sends signals to move the print head to compensate for any error in the feeding of the feed system. Compensating adjustments are then made to the next subsequent substrate indexing step so that the print head tends to move back toward its home or zeroed position with its next correction and does not walk away from this home position as a result of cumulative movements. For printers that have bridges that are moveable relative to the machine frame on which the print head is carried, print head motion is achieved by moving the bridge, for example, by actuating a linear servo bridge motion system. For fixed bridge roll-to-roll printers, the print head can be caused to shift longitudinally on the bridge to make the correcting movements.
The controller for controlling the amount of error and the compensation thereof indicate the problems in obtaining accurate positioning where the bridgehead moves relative to the support area, the support area moves relative to the material to be printed, and the material to be printed is fed as well.
Thus, despite the developments described above, there is a need for a simple, reliable printing machine that is capable of accurately printing onto continuous substrate roll-to-roll in a first mode, or onto single sheets in a second mode, where conversion of the machine from one mode to the other is relatively easy, and the present invention addresses this need.